Polyurethane film comprising graphene and preparation process thereof

Abstract

A polyurethane film comprising a polyurethane resin and graphene, wherein the graphene is present in an amount of 1 to 30% by weight on the total weight of the film and consists of graphene nano-platelets, wherein at least 90% has a lateral dimension (x, y) of 50 to 50000 nm and a thickness (z) of 0.34 to 50 nm, wherein the lateral dimension is always greater than the thickness (x, y>z), wherein the C/O ratio is ≥100:1, and a preparation process thereof.

Claims

1. A polyurethane film comprising a polyurethane resin and graphene, said graphene present in an amount of from 1% to 30% by weight of the polyurethane film, and said graphene consisting essentially of graphene nano-platelets, with at least 90% of the graphene nano-platelets having a lateral dimension of from about 50 nm to 50000 nm and a thickness of from about 0.34 nm to 50 nm, and with the lateral dimension greater than the thickness and a C/O ratio ≥100:1.

2. The polyurethane film of claim 1, further comprising from 0.1% to 5% by weight on the total weight of the polyurethane film of an antiblocking additive.

3. The polyurethane film of claim 1, further comprising at least two coupled layers, one of which is a film not comprising graphene.

4. The polyurethane film of claim 1, wherein the C/O ratio of said graphene nano-platelets is ≥200:1.

5. The polyurethane film of claim 1, wherein at least 90% of said graphene nano-platelets' lateral dimension is from 100 nm to 25000 nm and thickness from 0.34 nm to 20 nm.

6. The polyurethane film of claim 5, wherein at least 90% of said graphene nano-platelets' lateral dimension is from 500 nm to 15000 nm and thickness from 0.34 nm to 8 nm.

7. The polyurethane film of claim 1, wherein said graphene is present in an amount of from 2% to 25% by weight on the total weight of the polyurethane film.

8. The polyurethane film of claim 7, wherein said graphene is present in an amount of from 3% to 15% by weight on the total weight of the polyurethane film.

9. The polyurethane film of claim 2, wherein said antiblocking additive is selected from silica, silicone, and kaolin.

10. A method for the preparation of a polyurethane film comprising graphene, comprising the steps of: a) preparing a composition comprising: a1) a polyurethane resin or precursors thereof, a2) from 0.1% to 5% by weight of an antiblocking additive, a3) from 1% to 30% by weight of graphene consisting essentially of graphene nano-platelets, with at least 90% of the graphene nano-platelets having a lateral dimension of from about 50 nm to 50000 nm and a thickness of from about 0.34 nm to 50 nm, and with the lateral dimension greater than the thickness and a C/O ratio ≥100:1; (b) adjusting the viscosity of the composition of step (a) with a solvent to from about 4000 cPs to 15000 cPs; (c) applying the composition of step (b) to a flat support until a layer having a thickness of from about 10 μm to 100 μm is formed; (d) heating said layer at an increasing temperature of from about 30° C. to 180° C., whereby a polyurethane film is formed; and (e) detaching said polyurethane film from said support.

11. The method of claim 10, further comprising step (d1) following said step (d), in which the polyurethane film is coupled with another film not comprising graphene by passing through a calender, and step (d2) in which the two coupled films are heated at an increasing temperature between 30° C. and 180° C. to form a multilayer film.

12. The method of claim 11, wherein said film not comprising graphene is selected from the group consisting of polytetrafluoroethylene (PTFE), thermoplastic polyurethane (TPU), polyolefins, polyamides, and polyester.

13. The method of claim 10, wherein said antiblocking additive is selected from silica, silicone, and kaolin.

14. The method of claim 10, wherein said flat support used in said step (c) consists essentially of non-adhesive paper, optionally provided with a surface finish on the side on which said composition is applied.

15. A polyurethane film formed according to claim 10.

Description

(1) The invention will now be described also with reference to FIG. 1, which schematically illustrates the process according to the invention.

(2) The process for the preparation of a polyurethane film according to the invention comprises the following steps: (A) Prepare a composition comprising: a1) a polyurethane resin or precursors thereof, a2) 0.1 to 5% by weight of an antiblocking additive, a3) 1 to 30% by weight of graphene consisting of grapheme nano-platelets, in which at least 90% has a lateral dimension (x, y) of 50 to 50000 nm and a thickness (z) of 0.34 to 50 nm, in which the lateral dimension is always greater than the thickness (x, y>z), and in which the C/O ratio is ≥100:1; (B) Adjust the viscosity of the composition of step (A) by adding a solvent until obtaining a viscosity in the range from 4000 to 15000 cPs; (C) Apply the composition having the viscosity of step (B) on a flat support until forming a layer having a thickness of 10 to 100 μm; (D) Heat said layer to an increasing temperature between 30 and 180° C., with formation of a polyurethane film; (E) Detach said polyurethane film from said support.

(3) In step (A) the components a1), a2) and a3) are placed in a vessel provided with stirring system and mixed. Preferably a mechanical stirrer is used at a rotation speed of 100 to 2000 r.p.m., more preferably 150 to 100 r.p.m.

(4) Preferably the composition of step (A) also comprises a flow additive (component a4).

(5) The antiblocking additive a2) is as defined previously.

(6) In step (B) the viscosity of the mixture of a1), a2) and a3) is adjusted with the addition of an organic solvent in the range between 4000 and 15000 cPs, preferably between 6000 and 12000 cPs. Examples of said solvent are dimethylformamide, toluene, acetone, ethyl acetate and dipropylene glycol methyl ether, marketed under the brand Dowanol® DPM by Dow Chemical.

(7) The steps (C) to (E) are described with reference to FIG. 1.

(8) In FIG. 1, the number 10 indicates a roll of paper adapted to constitute the support tape on which the composition prepared in steps (A) and (B) is applied, known in the sector as release paper or casting & release paper. This paper has non-adhesion characteristics, on which the polyurethane film is formed, and from which it can then be detached and separated, due to the non-adhesion characteristics and the particular surface finish of the paper.

(9) In step (C) the roll of release paper 10 is unwound in the direction of the arrow A at an appropriate speed, for example between 3 and 30 m/min, and a controlled amount of composition prepared in steps (A) and (B) is deposited on the paper in continuous mode. The thickness of the layer thus formed is defined by adjusting the distance between the paper tape and a blade 14 positioned on top of it. Typical thicknesses are, for example, between 10 and 100 mμ.

(10) In step (D) the paper tape on which the layer of polyurethane composition having the desired thickness has been deposited is introduced into an oven 16 and heated to an increasing temperature between 30 and 180° C., with formation of a polyurethane film.

(11) In the following step (E) the film is detached from the release paper tape and wound on a roller, in a manner not illustrated in FIG. 1 but known to a person skilled in the art.

(12) In the preparation of a multilayer film, the process comprises, after the heating step (D), coupling of the polyurethane film prepared according to steps (A) to (D) with at least one other resin layer or film 18, thus providing intermediate coupling (D.sub.1) and heating (D.sub.2) steps, obtaining a multilayer film, and subsequent step (E) of detaching the multilayer film from the support. The film 18 consists of a second polyurethane film not containing graphene, or a film consisting of a different resin, not comprising graphene. Suitable resins consist, for example, of polytetrafluoroethylene (PTFE), thermoplastic polyurethane (TPU), polyolefins (polypropylene, polyethylene), polyamide and polyester.

(13) The thickness of the film 18 coupled to the polyurethane film comprising graphene is usually between 10 and 100 μm.

(14) The film 18, wound on a roller, is unwound and laid on the polyurethane film coming out of the oven 16 and coupled to the same by passing through a calender 20, according to step (D.sub.1). The bond consisting of the release paper+polyurethane film comprising graphene+second film is sent to a second oven 22, where it is heated to a temperature between 100 and 160° C., according to step (D.sub.2).

(15) At the outlet of the oven 22, step (E) is carried out, in which the release paper is separated and wound on a roll 10′, while the two-layer film 24 consisting of the polyurethane film comprising graphene and the second film coupled to it is wound on a tape 26.

(16) The monolayer or multilayer polyurethane film comprising graphene according to the invention shows properties superior to the known films, and can therefore be advantageously used for the production of articles in various technological sectors, such as the clothing sector, particularly clothing and sports equipment, footwear, workwear and wearable electronics, furnishing and the industrial sector.

(17) In one embodiment, the film according to the invention is a three-layer film, one layer of which consists of the polyurethane film comprising graphene, another consists of a film not comprising graphene, and the third consists of a thermoadhesive material, also not comprising graphene.

(18) In another embodiment, the film according to the invention is a two-layer film, one layer of which consists of the polyurethane film comprising graphene, another consists of a film not comprising graphene, and the release paper used for preparing the polyurethane film comprising graphene has a particular surface finish, which can transfer to the film comprising graphene a particular aesthetic appearance, for example opaque black, defined as carbon look.

(19) The following examples illustrate some embodiments of the invention and are provided by way of non-limiting example.

EXAMPLES

Example 1

(20) Preparation of a Polyurethane Monolayer Film

(21) Step (A)

(22) 100 kg of polyurethane resin (ICAFLEX BR447 MATT3) are placed in a vessel provided with a mechanical stirrer (Dissolver DISPERMAT® CN100, diameter of heavy duty disc 350 mm) and the rotation speed is adjusted to 200 r.p.m. The following are then added: 5 kg of G+ graphene powder marketed by Directa Plus SpA, consisting of nano-platelets having a lateral dimension of 1 to 7 μm, a thickness of 0.34 to 4 nm, and a C/O ratio >100 0.8 kg of silica (OK 500) 2.7 kg of isocyanate catalyst (TRIXENE DP9B1376) 0.5 kg of flow additive (ADITEX LA 77)

(23) Step (B)

(24) A solvent consisting of dipropylene glycol methyl ether marketed under the brand Dowanol® DPM by Dow Chemical is added to the composition of Step (A) and the viscosity is brought to the range 6,000-10,000 cPs. The mixture is stirred at 1000 r.p.m. for 1.5 hours.

(25) Step (C)

(26) In a coating line as shown in FIG. 1 the polyurethane composition formed in step (C) is uniformly applied on a roll of release paper (S/K VEZ Matte, SAPPI) by means of a pneumatic pump that withdraws the composition from the stirred vessel. The roll of release paper is fed forward at a speed of 10 m/min. The thickness of the polyurethane film is set to 20 μm by adjusting the gap between the paper and the blade 14.

(27) Step (D)

(28) The paper tape on which the layer of polyurethane composition with thickness of 20 μm has been deposited is placed in the oven 16 and heated to an increasing temperature between 40 and 160° C., with formation of a polyurethane film.

(29) Step (E)

(30) At the outlet of the oven 16 a flap of polyurethane film is detached by hand, and then attached to a cylinder to be wound. Also the release paper is wound on a cylinder and separated from the film. At the system outlet a check is performed on the uniformity of the weight between centre and edges by weighing a 100 cm.sup.2 disc with 0.001 precision balance.

(31) The film has a graphene content of approximately 5% by weight and a silica content of approximately 0.8% by weight.

(32) Characterization of the Film Formed Breathability: RET <10 m.sup.2 Pa/W (ISO 31092,) Impermeability: >1500 mm (ISO 20811) Abrasion resistance: >5000 cycles (ISO 12947) Surface resistivity: 7000Ω/γ (JIS K 7194 standard) In-plane thermal conductivity: 3.213 W/mK (ISO 22007-2) IR absorbance: Absorption >90% Antibacterial properties: Bacteriostatic on both gram positive and gram negative bacteria (UNI EN ISO 20743:2013)

(33) The surface resistivity is a parameter that characterizes the electrical conduction properties, for two-dimensional or almost two-dimensional samples, i.e. having thickness much smaller than the width and the length. The surface resistivity is defined as the ratio between the electrical resistivity and the thickness. The electrical resistivity is the reciprocal of the electrical conductivity.

Example 2

(34) Preparation of a Two-Layer Film of Polyurethane and PTFE

(35) Steps (A) to (D) are performed as in Example 1, the only difference being that in Step (A) the amount of graphene is 3 kg and the amount of silica is 0.5 kg.

(36) The film obtained has a graphene content of approximately 3% by weight and a silica content of approximately 0.5% by weight.

(37) At the outlet of the oven 16 a roll of a film 18 of PTFE without graphene (MS-2020, Membrane Solutions), thickness 25 μm, is positioned on a support. The PTFE film 18 is placed over and laid on the polyurethane film coming from the oven 16. The bond consisting of the release paper+polyurethane film comprising graphene+PTFE film 18 is passed through a calender 20 (step D.sub.1) and then sent to a second oven where it is heated to a temperature of 160° C. (step D.sub.2).

(38) At the outlet of the oven 22 the release paper is separated and wound on a roll 10′, while the two-layer film 24 consisting of the polyurethane film comprising graphene and the PTFE film coupled to it is wound on a tape 26 (step E).

(39) At the system outlet the uniformity of the weight between centre and edges is checked (a 100 cm.sup.2 disc is weighed with 0.001 precision balance).

(40) Characterization of the Two-Layer Film Formed Breathability: RET <7 (method RET, ISO 31092, m.sup.2 Pa/W) Impermeability: >20000 mm (ISO 20811) Abrasion resistance: >45000 cycles (ISO 12947) Surface resistivity: 43000Ω/□ (JIS K 7194 standard) Thermal in-plane conductivity: 2.404 W/mK (ISO 22007-2) IR absorbance: Absorbance >90% Antibacterial properties: Bacteriostatic on both gram positive and gram negative bacteria (UNI EN ISO 20743:2013)

Example 3

(41) Preparation of a Polyurethane Two-Layer Film

(42) The operating procedure is the same as in Example 2, with the following differences: in Step (A) the amount of graphene is 10 kg, the amount of silica is 1.3 kg and the polyurethane resin WITCOFLEX 886 MATT was used. At the outlet of the oven 16 the polyurethane film containing graphene, which has a graphene content of approximately 10% by weight and silica content of approximately 1.3% by weight, is coupled not with a PTFE film but with another polyurethane film without graphene, having thickness of 20 μm.

(43) The other aspects of the procedure are as described in Example 2.

(44) Characterization of the Two-Layer Film Formed Breathability: RET <25 (method RET, ISO 31092, m.sup.2 Pa/W) Impermeability: >10000 mm (ISO 20811) Abrasion resistance: >50000 cycles (ISO 12947) Surface resistivity: 834Ω/γ (JIS K 7194 standard) In-plane thermal conductivity: 6.285 W/mK (ISO 22007-2) IR absorbance: Absorption >90% Antibacterial properties: Bacteriostatic on both gram positive and gram negative bacteria (UNI EN ISO 20743:2013)

Example 4

(45) Preparation of a Thermoadhesive Tape Comprising a Two-Layer Polyurethane Film

(46) The operating procedure is the same as in Example 3, the only difference being that the release paper is not separated from the two-layer polyurethane film.

(47) The bond consisting of the two polyurethane films and the release paper is positioned at the beginning of the system and, on the polyurethane film not comprising graphene, a thermoadhesive material (TERMOFIX s 373) is applied, following the procedure of step (C).

(48) The other steps of the procedure are then performed as in Example 3. The three-layer film thus produced is then sliced with an appropriate blade to create thermoadhesive tapes with width of 2 cm.

Example 5

(49) Preparation of a Two-Layer Polyurethane Film with Carbon Look Finish

(50) Step (A)

(51) 100 kg of polyurethane resin (Texane SP 162 RB, TWS) are placed in a vessel provided with mechanical stirrer (Dissolver DISPERMAT® CN100, diameter of heavy duty disc 350 mm) and the rotation speed is adjusted to 500 r.p.m. The following are then added: 15 kg of graphene powder G+ sold by Directa Plus SpA, as per Example 1 0.5 kg of silica (OK 500) 3 kg of isocyanate catalyst (Texane D3) 2 kg of melamine catalyst (Texane M2) 1.5 kg of accelerator (Texane B5) 0.7 kg of flow additive (ADITEX LA 77)

(52) Step (B)

(53) A solvent consisting of dimethyl formamide is added to the composition of Step (A) and the viscosity is brought to the range 6,000-10,000 cPs. The mixture is stirred at 2000 r.p.m. for 2 hours.

(54) Step (C)

(55) In a coating system as in FIG. 1 the polyurethane composition formed in step (C) is uniformly applied on a roll of textured release paper (ULTRACAST, SAPPI) by means of a pneumatic pump which takes the composition from the stirred vessel. The roll of release paper is fed forward at a speed of 10 m/min. The thickness of the polyurethane film is set to 30 μm by adjusting the gap between the paper and the blade 14.

(56) The film obtained has a graphene content of approximately 15% by weight and a silica content of approximately 0.5% by weight.

(57) Step (D)

(58) The textured release paper tape on which the layer of polyurethane composition having thickness of 30 μm has been deposited is placed in the oven 16 and heated to an increasing temperature between 40 and 160° C., with formation of a polyurethane film.

(59) Steps (D.sub.1) and (D.sub.2) of the Process

(60) At the outlet of the oven 16 a roll of a polyurethane film 18 without graphene having thickness of 20 μm is positioned on a support. The film 18 is placed over and laid on the polyurethane film coming from the oven 16. The bond consisting of the textured release paper+polyurethane film comprising graphene+polyurethane film not comprising graphene 18 is passed through a calender 20 and then sent to a second oven 22, where it is heated to a temperature of 160° C.

(61) Step (E)

(62) At the outlet of the oven 22 the textured release paper is separated and wound in a roll 10′, while the two-layer film 24 consisting of the polyurethane film comprising graphene and the polyurethane film coupled to it is wound on a tape 26.

(63) At the system outlet the uniformity of the weight between centre and edges is checked (a 100 cm.sup.2 disc is weighed with 0.001 precision balance).

(64) The layer consisting of the polyurethane film comprising graphene has a carbon look finish.

(65) Characterization of the Two-Layer Film Formed Breathability: not breathable Impermeability: >10000 mm (ISO 20811) Abrasion resistance: >50000 cycles (ISO 12947) Surface resistivity: 170Ω/γ (JIS K 7194 standard) In-plane thermal conductivity: 8.082 W/mK (ISO 22007-2) IR absorbance: Absorption >90% Antibacterial properties: Bacteriostatic on both gram positive and gram negative bacteria (UNI EN ISO 20743:2013)

Example 6 (Comparison)

(66) Preparation of a Monolayer Polyurethane Film without Graphene

(67) Example 1 was repeated without using graphene.

(68) Characterization of the Film Formed Breathability: RET <7 (method RET, ISO 31092, m.sup.2 Pa/W) Impermeability: >10000 mm (ISO 20811) Abrasion resistance: >20000 cycles (ISO 12947) Surface resistivity: non conductive—non measurable (JIS K 7194 standard) In-plane thermal conductivity: 0.023 W/mK (ISO 22007-2) IR absorbance: <10% Antibacterial properties: Non bacteriostatic (UNI EN ISO 20743:2013)

(69) From the preceding description and from the examples, it is demonstrated that the use of grapheme nano-platelets having the characteristics defined in the present invention represents an effective tool for improving the characteristics of polyurethane film and membranes. In particular it is possible to: considerably improve the thermal conductivity of the film, in order to provide and exploit a planar thermal circuit to dissipate the heat and therefore increase the level of comfort of the item of clothing—in the case of film used in the clothing sector—or the performance level of the device incorporating the film; improve and modulate the electrical conductivity to achieve various performances of the film comprising antistatic effect (surface resistivity between 10.sup.10 and 10.sup.5 Ohm), heating and conducting effect (surface resistivity between 10.sup.4 and 10) and increase in absorption of infrared radiation to increase the insulating power of the film; give the film bacteriostatic properties.

(70) On the other hand, the examples demonstrate that the graphene has a negative impact on breathability (increases the RET) and on impermeability.